Diffuser tube



C. H. NORDELL DIFFUSER TUBE May 29, 1951 3 Sheets-Sheet 1 Filed Feb. 26, 1947 Elie/2Z5" Car/1f, J6722el5 iii? May 29, 1951 c. H. NORDELL DIFFUSER TUBE 3 Sheets-Sheet 2 Filed Feb. 26, 1947 C. H. NORDELL May 29, 1951 DIFFUSER TUBE 3 Sheets-Sheet 3 Filed Feb. 26, 1947 i'sion of gases.

Patented May 29, 1951 UNITED S TATES PATEN T F F ICE DIFFUSER Carl H. Nordell, Palm Springs, Calif.

Application February 26, 1947, Serial No. 730,931

used in the fabrication of porous diffusers, few

have been efiicient to an extent to warrant wide commercial use, and these generally "have not been entirely satisfactory in use. One type of porous diffuser of the prior art, which .proved impractical, was made of porous wood. Anothertype that found little use commercially, was made by pulling a slitted or needled-punctured rubber'sleeve-over a perforated, thick metalpipe. This type of diffuser proved to be impractical because of the weight thereof, and because of the very large and costly head losses developed in forcing the air through the normally closed openings in the rubber sleeve.

The most commonly used tubular air-diffusers of the prior art are made of porous --carbon and ceramic material, both natural and artificial. These carbon and ceramictubular diffusers "have been generally formed of packed granular -mate rial with the grains bonded to one another by cementing or sintering, the voids between the grains forming irregular passages for the emis- These porous tubesare of uncertain and non-uniform-structure, :and the resulting diffusion is necessarily likewiseuncertain and non uniform. The passages through these media are haphazard and tortuous and, for the sake of strength, there must be considerable thickness. In consequence, the diffusers are heavy and the air passages therethroug'h are verylong relative "to the diameter thereof. Considerable pressure is required to force "the -air or gas through the tortuous passages and the passages clog easily, either-from dust in the-air,

particles of scale, or rust from the air -main.

Additionally, pore clogging in the-ceramic tube 'is caused whenthe air supply is cut off, and the surrounding liquid 'backflows through the minute .passages, carrying with it bits of debris that .are not initially removed when the flow of-air is resumed.

Another .methodof forming diffuser tubes that metal tube, the "diffusionbccurring as a result o'fthe par'tialstoppage of "the *holes in the-foraminous core, and the chance labyrinth of passages formed between the coils and through the rope. The high head loss and the unsatisfactory charactor of the diffusion were the main factors re- :sponsible'for the impracticability of this diffuser tube. Another method of forming diffuser tubes which have proven to be impractical is to wind wire of circular cross section around a foraminated heavy metal tube.

I have discovered that the defects and objecvtions inherent in the prior art porous tubular diffusers are minimized and substantially eliminated by wrapping-a cord of non-circular cross section around a rigid, relatively light weight, :hollow core providi-ng that but one layer of wrapping is used and the coils tightly pressed to- -gether. The hollowcore is fabricated in a form in which flutes or corrugations are formed 1ong itudinallyacross this core. In the valleys of the corrugations ,or flutes, there are orifices "for controlling the passage of'air from the core'to the air spaces under the .cord windings. The cord that is used for winding around the hollow metal cores possesses helical grooves so that when ad- ,jacent coils are pressed tightly together, the grooves form minute slanting passages or pores ,of substantially uniform character and dimensions for the emission of air or gas, Thisform of cord can be formed by extruding a plastic-or by twisting two, three or more strands of textile or plastic cord into a cord of the desired thickness, in the same manner that a rope'isformed, It is obvious that the size and spacing ;of the .pores can be closely and positively controlled by selection 'of a cord of a desired size and by the tightness and compression of the winding,

The cord-wound diffuser of the invention, 1. e., the fiutedforaminated core and the winding, are fabricated from materials that are capableo'f re-. sisting deterioration "from *the'action of "the gas or liquid which may be present in the process in which these tubes are utilized.

The cord-wound diff-user tube of the present invention is characterized by its adaptability to be "fabricated in relatively "long lengths which "can be readily joined together into diffuser pipes of anydesired length. This feature permits the tubes to 'be combined into a diffuser and air main. However, to accomplish the combining effectof an air main and diffuser, the :rate of air feed along the length of the tube must be compensated for the loss of pressure aalong the pensation is good for any rate of flow since both the orifice loss and the friction loss will vary together, that is to say, as the square of the rates of air feed.

If the compensation is made by elevating the far end of the diffuser main, and thus reducing the outside hydrostatic pressure, the compensation will only give uniform diffusion for one particular rate of air flow. This method has a very apparent advantage. As for example, if the air main or diffuser tube is so set that the loss of pressure is compensated at'a low rate of air flow, there would then be a uniform rate of diffusion along the tank when a rate of air feed was low, and presumably when the sewage was weak, as at night. When the strength of the sewage and the desired rate of air flow increased, there would be more loss along the line which would mean that the head end of the tank would receive a greater proportion of the air flow. In other words, this arrangement would lead to tapered aeration during the high flow, and uniform aeration at night. This then would be an automatically modulated tapered I aeration process.

' liquid in which it is immersed. The lightness in weight combined with the diffuser-air main feature, produces a construction that is inexpensive to manufacture and very simple in its installation.

In such an installation, the diffuser mains, one or more in spaced realtion, as desired, would I lie parallel to and adjacent the aeration tank wall. In a typical aeration tank of the activated sludge process of treating sewage, in a space of some 2 feet above the level of the diffuser main, mixing of the alternate bands of rising air bubbles and water and risin bands of solid water takes place. There is some advantage in placing the difiuser mains parallel to the tank wall because the lateral sweep of the water toward the wall effects thorough mixing and distribution somewhat more rapidly than would be the case where the tubes are perpendicular to the wall.

An important feature of the new diffuser tube is the uniformity of distribution of the gas or vapor across the length of the tube. It has been found that when air is being discharged through a diffuser tube at a non-uniform rate throughout its length, there are areas of excessive discharge which cause the air bubbles to coalesce in these areas. In consequence, the air is not uniformly dispersed throughout the liquid surrounding the tube, and the system does not operate at a maximum efficiency. With the diffuser tube of the present invention, the uni-' formity of air diffusion through each tube can be controlled very closely by the amount of compression and tension that is put upon the cord when wrapping around the hollow metal core,

thus producing a very uniform diffusion and enabling the systems in which they are used to operate at a maximum efficiency.

A problem that has always been present when utilizing diffuser tubes is the matter of head loss. In the diffuser tube of my invention, the head loss is relatively low, due to the character and the very short length of the pores through which the air passes from the tube to the liquid.

The structures by which the various results are attained will be described in connection with the accompanying drawings, in which:

Figure l is a fragmentary perspective view of an air main with a plurality of diffuser tubes embodying the invention extending therefrom;

Fig. 2 is an enlarged view of one of the diffuser tubes showing the twisted strand cord about the foraminated core, partly in elevation and partly in section;

Fig. 3 is a longitudinal sectional view taken along the line33 of Fig. 2;

Fig. 4 is a cross sectional view taken along the line 4-4 of Fig. 3;

Fig. 5 is a highly magnified longitudinal sectional view taken along the line 55 of Fig. 4;

Fig. 6 is a greatly enlarged side elevational view of a mono-filament cord which may be used in accordance with the present invention;

Fig. '7 is a magnified longitudinal sectional view, similar to Fig. 5, showing the cross sectional configuration of the mono-filament cord;

Fig. 8 is an enlarged side elevational view of a modified form of diffuser tube having intermittent longitudinal flutings;

Fig. 8a is a longitudinal sectional view taken along the line 8a-8a of Fig. 8;

Fig. 9 is a view, partly in section and partly in elevation, showing an elongated modified form of diffuser tube;

Fig. 9a is a longitudinal sectional view taken along the line 9a9a of Fig. 9;

Fig. 10 is a cross sectional view taken along the line lO-ll] of Fig. 9;

Fig. 11 is a cross sectional view taken along the line llll of Fig. 9;

Fig. 12 is a fragmentary longitudinal sectional view showing a plurality of diffuser cores joined together to form elongated units which are clamped together to form diffuser mains of any required length;

Fig. 13 is a cross sectional view taken along the line l3l3 of Fig. 12;

Fig. 14 is an enlarged fragmentary longitudinal sectional view showing the means for clamping together lengths of diffuser cores; and

Fig. 15 is a cross sectional view taken along the line i5-l 5 of Fig. 14.

In the drawings, the reference numeral 2 indicates an air main having a plurality of threaded core is an open ended cylindrical tube to the ends of which caps 1 and 8 are secured in any suitable manner, preferably by welding. End cap 1 has a pair of apertures 9 and 9' through which the starting end of cord winding 6 is threaded and knotted, as indicated at in, to provide a firm anchor for the winding. End cap 8 has an exteriorly threaded neck I l which fits into threaded opening 3 in the air main. A bolt 12 is threaded i into end cap 8 to provide an anchor for the end of the cord winding. After the end of the cord is wrapped around the stem of the bolt l2 the bolt is screwed down to hold the cord securely. Core 5 is fluted to provide alternate ridges I3 and valleys i4 extending longitudinally of the core. One or more orifices l5 are provided in each of the valleys for the passage of air or gas from the inside of the core through the winding.

. ing liquid.

The cord, which is in close contact with the ridges on the core, cooperates with each valley to form individual air spaces. The flow'of air into these spaces is controlled by the orifices. Preferably one or two orifices are provided for each two feet of valley for more effective control.

The cord wound around the outside of the core may be formed 'of two ormore strands of suitable material twisted into rope form. The preferred cord is formed of three strands of material twisted together as shown. The interstices between the twisted strands of cord when the latter is wound about the core form slanting pores through which the air which has passed from the inside of the core through orifices l passes in a diffused state from the pores into the surround- The cross sectional area of these slanting pores can be accurately controlled by employing a cord of uniform, non-circular crosssection, winding it under uniform tension, and

- compressing the winding uniformly along the length of the tube. I

In winding the cord on the core it is important to use only one layer of cord because the character and size of the path made by the interstices of the strands can thereby be accurately controlled by the compressive force used to squeeze the coils together. The addition of a second layer of cord causes the first layer to be flattened out somewhat and the accuracy of pore size control is lost. Furthermore, the head loss is greatly increased because the air must force its way through the pores of two layers, and the pores of the second layer are not necessarily a direct continuation of the pores of the first layer. This latter fact causes the diffusion to be uneven when two layers of cord are used. The increased head loss and the unevenness of the diffusion makes the use of tubes wound with two layers of cord prohibitively expensive.

The cord may be formed of any suitable material, textile or plastic, capable of withstanding the corrosive effects of the liquid with which it is to be brought in contact. A preferred material is a vinyl resin of the type commercially known as "Saran which is formed from a copolymer of vinyl chloride and vinylidine chloride. It will be obvious that any number of strands,'not less than two, may be used in forming the cord. The cross sectional configuration of the cord formed from three twisted strands of Saran is clearly shown in Fig. 5.

The cord may be a mono-filament of Sarah or similar material, as shown at IS, in Figs. 6 and '7. This cord is formed by extrusion of the plastic while in a thermoplastic state with a plurality of helical grooves I! (here shown with three grooves) extending longitudinally of the cord. If desired, the grooves may be straight and the cord twisted as it is wound around the core. In either case the paths formed by the grooves can be controlled as in the case of the multistrand cord so that the diffusion of the air is substantially uniform throughout the length of the tube.

The use of a cord of non-circular cross section, as exemplified by both the multi-strand cordshownin Fig. 5 and the mono-filament cord shown in Fig. 7, is of particular importance because it is this non-circular shape that causes the formation of tortuous paths that are-small enough to cause difiusion of the air passing therethrough. The advantages of the non-circular cross sectional area can best be appreciated by comparison of the results attained with those ill 6 attained by wrapping wire of circular cross sec"-- tion around a similar core. With the latter structure the air passages formed between adjacent convolutions of wire may be regular, but they-are very long in comparison to their widths, and'are essentially continuous slits. Much larger bubbles are emitted from a long slit thanfrom a seriesof pores of equal area, with the result that coalescence occurs. The cord of non-circular crosssection used in accordance with the present inventioh forms pores of substantiallycircul'ar or elliptical cross section so spaced apart that the streams of bubbles emitted by them do not coalesce.

In Figs. 8 and 8a a modified formo f diffuser tube I8 is shown in which a plurality "of intermittently spaced depressions l9 extendinglongitudinally of the diffuser are provided by fembossing or otherwise forming the core. Orifices 20, similar to orifices [5 are provided in the-bottom of each depression and end caps l and 8 are'p'r'ovided to close the ends as in the case of the diffuser of Fig. 2. The core may becovered with a single windin of cord, which maybe either multi-strand or mono-filament, as described above. g

The diffuser 2|, illustrated in Fig. 9, differs from that shown in Fig. 8 onl in that it is of greater length. The increased length may be obtained by forming a longer core with intermediate circumferential stiffening ribs 22 or by welding together a plurality of shorter cores. End caps 23 and 24, similar to end caps -l and 8, respectively, are secured to opposite ends of diffuser 2|.

- The cord 25 maybe wound continuouslyaround the entire length of the core, but it'is preferred to wind the cord in separate lengths with the'starting en'd secured to end cap 23 as described in connection with Figs. 2 and 3, in the case of the length adjacent that end, and to the ribs 22 by a knot'26 (Fig. 9a), in the case of the succeeding lengths. The other end of the cord for-each core section is secured to the stiffening rib 'at the end of each section except the last section, and to'end cap 24 in the "case of the last section, as'by bolt 21.

in the embodiment of the invention shown in Figs. 12 to 15, there is shown an air diffuser pipe 28. This pipe'comprises a plurality of sections bolted together'as shown in Figs. 12 and 14. A washer or sealing gasket 39 is positioned between the ends of adjacent sections. Brackets 3! each comprise an inverted U-shaped portion 32 and two oppositely directed flanges 33 parallel to the surface of the pipe sections, which are secured adjacent each end of each section by welding, as shown in Fig. 15. Clamping bolts 34 pass through brackets 3! on adjacent pipe se'ctions and secure the sections together. Each pipe section comprises a plurality of smaller sections welded together-at their ends, as indicated at35, Fig. 12. Each pipe section is fluted, the valleys provided with orifices and the ridges covered by a single layer of cord, as described above.

From the foregoing it will be seen that I have devised a new and improved diffuser in whichthe diffusion of air or gas there through can be regulated with great accuracy. The diffuser pipe may be fabricated in any desirable length. While I have described a few preferred embodiments of my invention in considerable detail it will'be understood that the description is intended "to be illustrative, ratherthan restrictive, as many details may be modified or changed without departing from the spirit or scope of the invention. Ac-

exact structures described, except as cordingly, I do not intend to be restricted to the limited by the appended claims. I v

I claim:

1. A diffuser tube comprising a hollow core having an inlet for air or a gas, a plurality of orifices in said core, a covering of compressible monofilament cord coiled tightly around said core with the coils pressed tightly together, and means to hold said cord on said core in the said tightly pressed condition, said cord having a plurality of helical grooves extending longitudinally in substantially parallel relationship, whereby the interstices between adjacent convolutions of said cord form substantially uniform pores for the emission of an aeriform body passing through said orifices.

2. A diffuser tube comprising a perforated hollow core having an inlet for air or a gas, and a single layer of compressible cord coiled tightly around said core with the coils pressed tightly together and with the compressed sides of adjacent convolutions of said cord in contact with each other, said cord having a plurality of helical grooves extending longitudinally in substantially parallel relationship, whereby the interstices between adjacent convolutions of said cord form substantially uniform pores for the emission of air passing through said orifices, and means to hold said cord about said core in the aforesaid tightly coiled state.

3. A difiuser tube comprising a perforated hollow core having an inlet for air or a gas, and a single layer of compressible cord coiled tightly around said core with the coils pressed tightly together and with the compressed sides of adjacent convolutions of said cord in contact with each other, said cord having a non-circular cross section formed by a plurality of helical grooves extending longtudinally in substantially parallel relationship, whereby the interstices between adjacent convolutions of said cord form substantially uniform pores for the emission of air passing through said orifices, and means to hold said cord about said core in the aforesaid tightly coiled state.

4. A diffuser tube comprising a perforated hollow core having an inlet for air or a gas, and a twisted, multi-strand, compressible cord coiled tightly around said core in a single layer with the coils pressed tightly together and with the compressed sides of adjacent convolutions of said cord in contact with each other, whereby the interstices between adjacent convolutions of said cord form substantiall uniform pores for the emission of air passing through said orifices, and means to hold said cord about said core in the aforesaid tightly coiled state.

5. A diffuser tube comprising a plurality of core sections each of which has an inlet for air or a gas and each of which is perforated for the passage of said aeriform body, said core sections being secured together in end to end relationship, and a single layer of compressible cord wrapped tightly around each of said sections with the coils pressed tightly together and with the compressed sides of adjacent convolutions of said cord on each of said sections in contact with each other, the cord on each of said sections having a plurality of helical grooves extending longitudinally in substantially parallel relationship, whereby the interstices between adjacent convolutions of said cord form substantially uniform pores for the emission of air passing through said-perforations, and means to hold the cord of each of said sections about said sections in the aforesaid tightly coiled state.

6. A diffuser tube comprising a plurality of core sections each of which has an inlet for air or a gas and each of which is perforated for the passage of said aeriform body, said core sections being secured together in end to end relationship, and a single layer of a twisted, multi-strand compressible cord coiled tightly around each of said sections with the coils pressed tightly together and with the compressed sides of adjacent convolutions of said cord on each of said sections in contact with each other, whereby the interstices between adjacent convolutions of said cord from substantially uniform pores for the emission of air passin through said perforations, and means to hold said cord about each of said sections in the aforesaid tightly coiled state. 7. A diffuser tube comprising a hollow core having an inlet for air or a gas, said core being fluted to form ridges and valleys extending longitudinally of said core, each of said valleys having an orifice for the passage of an aeriform body from inside said core, and a single layer of compressible cord wound tightly around said core with the coils pressed tightly together and with the compressed sides of adjacent convolutions of said cord in contact with each other, said cord having a non-circular cross section formed by a plurality of helical grooves extending longitudinally in substantially parallel relationship, whereby the interstices between adjacent convolutions of said cord form substantially uniform pores for the emission of an aeriform body passing through said orifices, and means to hold said cord about said core in the aforesaid tightly coiled state.

8. A diffuser tube comprising a hollow core having an inlet for air or a gas, said core having portions of its exterior surface depressed relative to the rest of said core, orifices extending through said depressed portions, and a single layer of compressible cord wound tightly around said core with the coils pressed tightly together and with the compressed sides of adjacent convolutions of said cord in contact with each other,

said cord having a non-circular cross section formed by a plurality of helical grooves extending longitudinally in substantially parallel relationship, whereby the interstices between adjacent convolutions of said cord form substantially uniform pores for the emission of an aeriform body passing through said orifices, and means to hold said cord about said core in the aforesaid tightly coiled state.

CARL H. NORDELL.

REFERENCES CITED The following references areof record in the file of this patent:

UNITED STATES PATENTS Number Name Date 713,544 Ware Nov. 11, 1902 1,317,463 Terry Sept. 30, 1919 1,473,160 Robbins Nov. 6, 1923 1,810,394 Dyhr June 16-, 1931 2,063,480 Braem Dec. 8, 1936 2,328,655 Lannert Sept. 7, 1943.

FOREIGN PATENTS Number Country Date 431,674 Great Britain July 12, 1935 

